A rotating electrical machine for a vehicle, e.g., a drive motor for a hybrid electric vehicle, needs acceleration performance such as start performance and passing performance, and instantaneous acceleration torque is, therefore, required of the motor.
In a case of a rotating electrical machine used for automobile application, a permanent magnet rotating electrical machine is used as a motor order to generate this instantaneous acceleration torque, and the generation of instantaneous, highly responsive torque is achieved by carrying a high current. The use of the high current described above, however, entails a problem of the loss of circuits in switching elements and bus bars of an inverter, resulting in an increase in the volume of the inverter for the need to take measures against generation of heat.
Owing to this, it is desired to reduce current in the inverter at the time of the generation of instantaneous torque, that is, to improve torque characteristics of the permanent magnet rotating electrical machine.
The torque components of the permanent magnet rotating electrical machine are roughly divided into magnet torque which is represented as a product of magnetic flux of the permanent magnet and the carried current and reluctance torque which is generated by the difference between d-axis reluctance and q-axis reluctance of a rotor. Improvement of the torque characteristics of the permanent magnet rotating electrical machine may be paraphrased as improvement of these torque components.
In order to increase the aforementioned magnetic torque components, it is a short cut to configuring the permanent magnet rotating electrical machine to make the surface area of the permanent magnets larger and to increase the magnetic flux of the permanent magnets. Specifically, a common practice is to increase the size of the rotating electrical machine.
However, in considering that vehicle fuel consumption increases in proportion to a vehicle body weight, it is essential to reduce the vehicle body weight to meet the recent demands for reducing environmental loads. Specifically, it is strongly desired to achieve downsizing and lighter weight including mounting space restriction for any of the components including the rotating electrical machine installed in a vehicle body. Specifically, even for the rotating electrical machine, size increase is not an option for the improvement of torque.
In relation to the aforementioned, Patent Literature 1 discloses a technique for utilizing reluctance torque and magnetic torque.